There is much indirect evidence in favor of the concept that male hormone action in target organs is expressed by intracellular metabolites of the circulating androgens. Control mechanisms for enzymes which affect the synthesis of these "active metabolites" may also regulate the hormone responsiveness of accessory reproductive structures and thus have an important bearing on the development of benign hypertrophy and adenocarcinoma of the prostate gland. Both the canine and human prostate have an age-dependent tendency to develop these conditions. We are therefore conducting comparative morphologic and biochemical experiments with organ and cell cultures of immature and mature normal, hypertrophic and neoplatic canine and human prostate and epididymis. We are studying (i) conditions for testosterone-dependent maintenance of the morphology of these organs in culture (ii) radiometabolite patterns after exposing the maintained cultures to C19- steroid radiosubstrates (iii) the effect of these tissue metabolites and of exogenous agents on the morphology and specialized biochemical functions of the explants and (iv) C19-steroid metabolism by the MA 160 line of human prostatic cells.